Field of the Invention
The disclosed and claimed concept relates to a circuit breaker with a visible disconnect switch and, more specifically, to a visible disconnect switch interlock assembly.
Background Information
Circuit breaker assemblies (CBA) provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. Typically, circuit breakers include a trip device and an operating mechanism. The trip device detects an over-current condition and actuate the operating mechanism. The operating mechanism opens and closes, either manually or in response to the trip device, a number of electrical contacts. In particular, vacuum circuit interrupters include separable main contacts disposed within an insulated and/or hermetically sealed housing. Generally, one of the contacts is fixed relative to both the housing and to an external electrical conductor. The other contact is moveable. In the case of a vacuum circuit interrupter, the moveable contact assembly usually comprises a pole stem of circular cross-section, an insulator member, a biasing device (e.g., a spring) and a contact member. The contact member includes, and is typically unitary with, a contact stem. The contact member and the contact stem are enclosed within the vacuum chamber. The contact member is coupled, directly coupled or fixed to the insulator member. The biasing device is disposed between the pole stem and the contact member. The pole stem is coupled to the operating mechanism external to the vacuum chamber. The operating mechanism includes compression springs operatively coupled to a pole shaft which is, in turn, operatively coupled to the movable contact. When the operating mechanism is actuated, the moveable contacts move between a first, open position, wherein the movable contacts are separated and not in electrical communication with the fixed contacts, and a closed, second position, wherein the movable contacts are coupled or directly coupled to, and are in electrical communication with the fixed contacts.
Over time the contacts are subject to wear and tear which diminishes the thickness of the contact assemblies. As the contact members are disposed in the vacuum chamber, the contact members cannot be seen. While there are tools and methods to determine contact wear, see, e.g., U.S. Pat. No. 6,150,625, issued Nov. 21, 2000, such constructs are not incorporated into the circuit breaker and cannot interact therewith. Further, such constructs provide for a determination of contact wear only when used and do not provide continuous check on the contact characteristics. The contacts may wear between checks performed during the scheduled maintenance or downtime.
The “displacement,” as used herein, of the second contact assembly is measured as the combination of the “stroke” and the “wipe.” That is, the “stroke” is the distance traveled by the movable contact assembly, and more specifically the pole stem, caused by the operating mechanism. The stroke is substantially a fixed distance related to the motion of the operating mechanism. The “wipe” is the movement between the insulator and the pole stem during which a contact spring is compressed. This motion is caused by the second contact assembly biasing device. As such, the “wipe” also has an associated force. Wipe and stroke are thus generally related to each other by relation: total displacement=stroke+wipe. As the contact assemblies erode, the stroke increases and wipe distance decreases and the wipe force decreases.
Further, the circuit breaker assembly may include a disconnect switch (DS) or a visible disconnect switch (VDS). It is understood that any discussion relating to a VDS is also applicable to a DS and that the following discussion uses a VDS as an example. A visible disconnect switch is a switch assembly structured to decouple the circuit breaker assembly from either the line or load conductors. That is, a visible disconnect switch is coupled to, and in electrical communication with, either the line or load terminals of the circuit breaker assembly. The visible disconnect switch includes a fixed contact that is coupled, directly coupled, or fixed to either the line or load terminals of the circuit breaker assembly. The visible disconnect switch further includes a movable contact that moves between a first position, wherein the VDS contact assembly second contact is spaced from, and not in electrical communication with, the VDS contact assembly first contact, and a second position, wherein the VDS contact assembly second contact is coupled to, and in electrical communication with, the VDS contact assembly first contact. The visible disconnect switch further includes an activating assembly structured to move the VDS second contact(s) between the first and second position.
It is not desirable, however, to move the visible disconnect switch between the first and second positions when the circuit breaker assembly contacts are in their closed, second positions. Further, it is not desirable to move the circuit breaker assembly contacts between their first and second positions when the visible disconnect switch contacts are in their open, first positions.
Further, the coupling assemblies for known visible disconnect switches are cumbersome and limit the location of the visible disconnect switch. That is, known coupling assemblies for known visible disconnect switches have a substantial number of fasteners and require the visible disconnect switch to be coupled to either the line side or the load side of the circuit breaker.
Accordingly, there is a need for a VDS interlock assembly movable between a CBA, first lockout position, wherein the CBA second contact assembly cannot move when the VDS second contact assembly is in the first position, and a VDS, second lockout position, wherein the VDS second contact assembly cannot move when the CBA second contact assembly is in the second position.
There is a further need for a contact wear indicator assembly that constantly measures contact wear, stroke and wipe, and communicates to the switchgear or control room during each circuit breaker operation for continuous monitoring of the contact health.
There is a further need for a contact wear indicator assembly to be compatible with existing circuit breakers.